The present invention relates generally to a tubular lining material for underground pipelines and the like, and more specifically, relates to a method for relining an underground pipe in situ which utilizes a seamless, expandable fabric liner which expands radially along its length throughout the underground pipe to form a new lining within the existing pipe.
The present invention finds its greatest utility in the area of underground pipeline repair and reconstruction. The most common underground pipeline is a sewer which conveys wastewater from residences and businesses to various collection points of a wastewater collection system and eventually lead to the wastewater treatment facility. Typically, sewers are buried underground and are typically located between streets and roadways. Due to shifting of the earth and secondary surface loadings, portions of the sewer system may become cracked or broken over time. These broken pipe sections compromise the ability and effectiveness of the sewer to accomplish its attended function, namely, the reliable conveyance of wastewater to a collection and treatment facility. Therefore, the prevention of obstructions in sewer pipeline systems is important.
Sewers may have their effectiveness compromised in other ways. For example, the inner surfaces of the sewer pipes may become eroded or at least roughened from continuous contact with wastewater and particularly, abrasive particles suspended therein which contact the interior surfaces of the sewer pipes. This erosion roughens the interior surface of the sewer pipe and consequently increases its pipe roughness coefficient, which is a measure of a pipe's resistance to fluid flow. The larger the roughness coefficient, the greater the head loss experienced by fluid flowing through the pipe. Thus, eroded pipes make it more difficult to convey wastewater than the pipes as originally installed. In order to reclaim the original design parameters of the sewer system, sewer pipes often need to be replaced or relined.
The above problems may be cured by either replacement or repair of the compromised sewer pipe portion. One means of sewer repair known in the art is to excavate the earth and roadway surrounding the broken portions and to replace the broken portions in their entirety. As one might expect, this solution is very expensive and labor-intensive and further leads to a disruption of the roadways and serious traffic problems. An inconvenience to the residence living in the area and utilizing those roadways. It therefore becomes desirable to effect repairs of sewer pipes in situ, i.e., within the underground pipe without excavation of the area surrounding the sewer.
Many method are known for the in situ relining of sewer pipes. Many of these methods utilize resin-coated liners which are inserted into the existing sewer pipe and unrolled against the sewer pipe. Once unrolled, the liner is held against the existing pipe while the resin is permitted to cure. After the resin cures, a new pipe is formed within the existing pipe add provides a new and relatively smooth interior surface having a low roughness coefficient which rivals or betters that of the original sewer pipe when first installed, protects the existing pipe from attack by chemicals found in wastewater effluent and reinforces the existing pipe to withstand external loading. Many of these in situ relining methods are described in the patent literature.
For example, British Patent Specification No. 1,340,068, published Dec. 5, 1973 describes one method of relining a sewer pipe which uses a liner made of a heavy needled felt stitched together along a seam to form an elongated tube which is then coated with a thermosetting resin. The resin-coated tube is wrapped around in an inflatable tubular bladder to form a liner-bladder assembly which is then inserted into a sewer. Hot water is pumped into the bladder to unroll the felt liner into the comprised portion of the sewer pipe. The bladder inflates under the water pressure and urges the felt against the inner surface of the sewer pipe. This particular type of process is not without disadvantages.
The seam is an inherent weak spot which may promote leakage of the resin, not only leading to waste of resin, but also inducing leaking in the cured-in-place pipe formed near the seam. Through the seam, leaking resin may contact and contaminate the hot water used to expand the inflatable bladder, which poses an environmental problem in that the water typically used in such a process for curing the resin is typically released into the environment when the bladder is deflated. In order to reinforce this seam, the British Patent Specification instructs one to overlap the edges of the felt liner along the seam. This overlapping increases the thickness of the liner extending the length of the seam, thereby resulting in an irregular cross-section of the relining sewer, which may adversely effect the flow characteristic of the reline pipe in a manner not expected by the designers or the installers. Additionally, because this heavy felt is not expandable, if the existing pipe has eroded to some extent, the diameter of the felt liner may not match the inner diameter of the existing pipe, and consequently where the felt liner does not contact the pipe wall, an annulus may be created which may become a weak point in the overall pipeline.
Another relining method known in the art is utilizes a plastic liner known as the NuPipe.RTM. liner, which is described in U.S. Pat. No. 4,867,921, issued Sep. 19, 1989. This liner is an extruded thermoplastic sleeve formed from polyvinyl chloride (PVC). The PVC liner is heated so that it softens and collapses, whereupon it is pulled through the sewer pipe. A rounding device is then propelled through the plastic liner to force the liner radially outwardly against the existing pipe. This process is not only costly, but also the PVC liner does not expand to any significant degree and accordingly, the installer needs to have a variety of different diameter liners on hand as inventory to effectively match the inner diameter of the existing pipe.
Yet another method of relining an existing sewer pipe includes the use of a woven textile liner which is laminated with multiple resin coatings. This type of liner construction and the method of installation of such a liner is described in numerous patents owned by Ashimori Industry Co., Limited of Japan. One such patent is U.S. Pat. No. 4,600,615, which issued Jul. 15, 1986 and which discloses an underground pipe relining material which consists of a woven air-impervious textile jacket. This textile jacket receives an outer resin coating consisting of multiple polyester resin layers laminated to each other. This construction is similar to that of a conventional fire hose. The production of this laminated outer coating is costly and complex, and it has been recognized in the pipe relining industry that such woven liners, like the fire hoses they emulate, do not expand significantly against the existing sewer pipe walls.
The tubular textile jacket disclosed in this and other Ashimori patents is a woven jacket which is woven on a loom and which utilizes circumferential fiber strands, known as warps, which enclose longitudinal fiber strands known as wefts. The warps substantially decrease the ability of the textile jacket to expand radially against the interior surface of the existing sewer pipe wall during the installation, because of this woven construction and because the liner fabric is intended to be impervious to air. This is a disadvantage because it requires an installation contractor to maintain large amounts of inventory of liners on hand which have different sizes of liners. This lack of expansion is a disadvantage when a compromised sewer pipe section which must be repaired has different diameter pipe sections. The existing pipe may have one diameter as indicated on engineering or installation drawings, while the actual diameter may in fact be lesser or greater at various points along the length of the pipeline. Additionally, the outer laminated resin coating restricts the flexibility of the liner.
Another disadvantage resides in the fact that because the radial expansion of these liners is so severely limited, in instances wherein the liner does not expand completely against the interior surface of the compromised sewer pipe, "tracking" occurs. Tracking is the movement of ground water which enters the space between the liner and the pipe from the surrounding earth and travels between the liner and the sewer pipe.
Another liner construction is disclosed in U.S. Pat. No. 4,723,579, which issued Feb. 9, 1988 and is also assigned to Ashimori Industry Co., Ltd. This patent discloses a complex, multi-layer liner construction which consists of two fabric layers, the first of which is an air-impervious first woven tube having a film of synthetic resin on its exterior surface and the second of which is a seamed, heavy felt that is coated with a binder and placed inside of the first woven tube. The second fabric tube has a series of open holes formed therein to assist in the impregnating of the outer woven tube with the resin binder.
Non-stretchable yarns are disclosed in this patent as comprising the first tube, which again exemplifies the non-expandable nature of woven fabric liners disclosed in Ashimori patents. With the woven fabric's inability to expand, the likelihood of tracking is increased and the installer must maintain a large inventory of woven tubes on hand.
Yet still another disadvantage to the resin cured in situ relining systems described above lies in the problem of resin migration, which is occurs when the resin applied to the liner may be partially dragged off of the liner when the liner assembly is drawn through the pipe or when the liner is inflated against a service connection and resin from the liner accumulates in the service connection. When the resin eventually cures, the liner is then consequently cut in the area of the service connection, but the resin may have migrated past the liner into the service connection and hardened to plug the service connection. Additionally where the liner is permeable, the resin may, during the time it is curing, emit unpleasant odors which may travel up service connections to customer households.
The present invention is therefore directed to an improved method of relining existing underground pipes which overcomes the aforementioned disadvantages.
In one principal aspect of the present invention, an improved method is disclosed for the relining of existing underground pipes which includes providing a liner in the form of a seamless fabric sleeve which is circularly and continuously knitted to define ground stitches and terry loop pile stitches extend from the ground stitches, the knitted construction of the sleeve providing it with radial expansion capabilities of upward to approximately one-third of its original diameter. The knitted liner has a diameter generally less than that of the existing pipeline and is saturated with a liquid resin and subsequently applied to an inflation member to form a relining assembly, which is inserted into the compromised section of the existing sewer pipe. The liner is installed in the existing sewer pipe by everting it so that the resin-impregnated liner opposes the interior surface of the sewer pipe. The resin-impregnated liner is then expanded in place to contact the existing pipe and conforms to the contour of the existing pipe without wrinkles forming in the liner which could affect the finished interior surface of the pipe lining. The resin is subsequently cured in place to form a new lining for the existing pipe section.
In another principal aspect of the present invention, a novel pipe liner is disclosed which comprises a circularly knitted seamless sleeve having defined ground stitches and multiple terry loop pile stitches extending out from the ground for a preselected length, the ground stitches forming a relatively smooth surface of the liner and the pile stitches forming a relatively rough surface of the liner. This pattern of stitching forms open areas between the stitches and imparts the fabric liner with a capability to expand upwards of at least one-third of its original diameter. The liner is saturated with a curable resin, such as a thermosetting polyester, epoxy or vinylester resin, and the open areas formed by the knit stitches permit the resin to thoroughly impregnate the entire fabric liner. The expansion capability of this liner and the fact that the resin is applied to the liner by impregnating, rather than a separate coating or layer, permits the liner to be everted through a pipeline without wrinkles forming in the liner during expansion and curing of the resin.
Yet still another principal aspect of the present invention, the fabric liner sleeve also includes an exterior flexible envelope along its length which provides a barrier between the interior pipe surface and the fabric liner sleeve during installation and subsequent curing to prevent the loss of resin during installation of the liner sleeve and to prevent resin build-up in service connections. This envelope comprises a urethane scrim which envelopes the fabric sleeve. The urethane scrim envelope may be used during the resin application step of the methods of the invention to form an enclosure to which a vacuum may be applied to accelerate the impregnation of the fabric liner sleeve by the resin.
In yet another principal aspect of the present invention, the liner has a composite multiple sleeve construction in which a first knitted fabric sleeve as described above has a second seamless fabric sleeve braided over the first fabric sleeve. The braided fabric sleeve provides reinforcement to the first knitted fabric sleeve and is capable of stretching in both the longitudinal and radial directions to match the expansion characteristics of the first knitted fabric sleeve.
In still another principal aspect of the present invention, a built-up liner is provided having multiple inner seamless knitted sleeves forming an interior portion of the liner in contact with a second seamless fabric braided fabric sleeve which forms an outer portion of the liner and which has a relatively rough surface profile. This multiple layer construction provides for a reinforced liner. The multiple sleeves all share similar expansion characteristics such that they expand together in unison to prevent the formation of wrinkles on the interior finished surface of the liner.
Accordingly, it is an object of the present invention, to provide a novel method for the relining of underground sewer pipes in which a seamless, knitted pile liner is impregnated with a resin and is expanded against the interior surface of the existing sewer pipe.
Another object of the present invention is to provide a liner for use in situ relining of underground pipes in which the liner includes a knitted fabric seamless inner tubular portion, the knit having a ground and a plurality of terry loop piles defined therein in which the piles extend outwardly from the ground, the liner further including a braided fabric seamless outer tubular portion, the interconnected braids preferably extending longitudinally along the liner, the liner further being saturated in a liquid resin which solidifies upon curing, the liner inner and outer portions being radially outwardly expandable when pressure is applied to the interior of the liner.
Another object of the present invention is to provide a method for the in situ relining of underground pipes comprising the steps of selecting a seamless fabric knitted liner, impregnating the fabric liner with a curable resin, inserting the resin-liner assembly into the underground pipe by everting the resin-liner assembly through the existing pipe, such that the liner turns inside out as it travels through the pipe to contact the interior surface of the pipe, expanding the resin-liner assembly against the interior surface of the underground pipe, and permitting the resin to cure in place while the liner is expanded to form a new pipe lining adjacent to and within the existing underground pipe, wherein the fabric liner is continuously knitted in a fashion having stitches that define a ground and stitches having a plurality of piles extending from the ground for a preselected height, the knitted liner being radially expandable from its original diameter whereby, when expanded, the liner conforms to the interior contour of the existing underground pipe.
It is still yet a further object of the present invention to provide a method for relining underground pipes as immediately described above and including the additional steps of enveloping the fabric liner in a urethane scrim envelope and placing the envelope between the pipe wall and the resin-liner assembly so as to provide a barrier between the pipe wall and the fabric liner which prevents the migration of resin during installation of the fabric sleeve and prevents resin build-up in service connections.
It is still another object of the present invention is to provide a reconstructed underground pipe having an original pipe member defining an interior pipe surface, a resin-impregnated liner disposed inside of and adjacent to the interior pipe adjacent to the original pipe interior pipe surface, the resin-impregnated liner including an expandable fabric liner in the form of a knitted, seamless tubular formed from a circularly knitted, crimped yarn knit into stitches defining a ground and stitches defining terry loop pile extending from the ground, the textile sleeve serving as a support for the resin.
Yet still another object of the present invention is to provide a liner for a pipeline having a separate outer, flexible, reinforced membrane which provides a vapor barrier and a resin shield for the liner during the installation and curing process of the liner and which further provides an envelope for use in impregnating the liner with a curable resin.
These and other objects, features and advantages of the present invention will be apparent for the following detail description, taken in conjunction with the accompanying drawings where in like reference numerals refer to like parts.